In the field of medical devices, glass, polymeric, and/or metallic materials are common substrate materials. These materials can be used for diagnostic devices or extracorporeal devices. With the exception of glass, many of the materials can be used for implantable devices.
Immobilization of biologically active entities on substrate materials in a biologically active form involves an appreciation of the respective chemistries of the entity and the substrate material. Modification of the chemical composition of a substrate material may be required to immobilize a biologically active entity thereon. This is usually accomplished by treating surfaces of the substrate material to generate a population of chemically reactive elements or groups, followed by immobilization of the biologically active entity with an appropriate protocol. With other substrate materials, surfaces of a substrate material are covered, or coated, with a material having reactive chemical groups incorporated therein. Biologically active entities are then immobilized on the substrate material through the reactive chemical groups of the covering material. A variety of schemes for covering, or coating, substrate materials have been described. Representative examples of biologically active entities immobilized to a substrate material with a covering, or coating, material are described in U.S. Pat. Nos. 4,810,784; 5,213,898; 5,897,955; 5,914,182; 5,916,585; and 6,461,665.
When biologically active compounds, compositions, or entities are immobilized, the biological activity of these “biologics” can be negatively impacted by the process of immobilization. The biological activity of many of biologics is dependent on the conformation (i.e., primary, secondary, tertiary, etc.) of the biologic in its immobilized state. In addition to a carefully selected immobilization process, chemical alterations to the biologic may be required for the biologic to be incorporated into the covering material with a conformation that renders the biologic sufficiently active to perform its intended function.
Despite an optimized covering and immobilization scheme, the biological activity of the immobilized biologic can be less than desired, particularly if additional processing, such as sterilization, is included. For implantable medical devices, sterilization is required prior to use. Sterilization may also be required for in vitro diagnostic devices having sensitivity to contaminants. Sterilization of such devices usually requires exposure of the devices to elevated temperature, pressure, and humidity, often for several cycles. In some instances, antibiotic agents, such as ethylene oxide gas (EtO) or vapor hydrogen peroxide are included in the sterilization process. In addition to sterilization, mechanical compaction and expansion, or long-term storage of an immobilized biologic can degrade the activity of the biologic.
There exists a need for medical devices having biologically active entities immobilized thereon without significant loss of biological activity, particularly when the immobilized biologically active entities are subjected to sterilization, mechanical compaction and expansion, and/or storage. Such a medical device would have biologically compatible compositions or compounds included with the immobilized biologically active entities that serve to minimize degradation of the biological activity of the entities during immobilization, sterilization, mechanical compaction and expansion, and/or storage. In some instances, the additional biologically compatible compositions or compounds would increase the biological activity of some biologically active entities following a sterilization procedure. Biologically active entities of particular interest for immobilization have anti-thrombotic properties.